```/* nag_sparse_nsym_precon_bdilu_solve (f11dgc) Example Program.
*
* Copyright 2014 Numerical Algorithms Group.
*
* Mark 24, 2013.
*/

#include <nag.h>
#include <nagf11.h>
#include <nag_stdlib.h>

static void overlap(Integer *n, Integer *nnz, Integer *irow, Integer *icol,
Integer *nb, Integer *istb, Integer *indb, Integer *lindb,
Integer *nover, Integer *iwork);

int main(void) {

/* Scalars */
double  dtolg, rnorm, tol;
Integer i, itn, k, la, lfillg, lindb, liwork, m, maxitn, mb, n, nb, nnz;
Integer nnzc, nover, exit_status = 0;
Nag_SparseNsym_Method method;
Nag_SparseNsym_Piv    pstrag;
Nag_SparseNsym_Fact   milug;

/* Arrays */
char    nag_enum_arg[40];
double  *a, *b, *dtol, *x;
Integer *icol, *idiag, *indb, *ipivp, *ipivq, *irow, *istb, *istr, *iwork;
Integer *lfill, *npivm;
Nag_SparseNsym_Piv  *pstrat;
Nag_SparseNsym_Fact *milu;

/* Nag Types */
NagError              fail;

/* Print example header */
printf("nag_sparse_nsym_precon_bdilu_solve (f11dgc) Example Program ");
printf("Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");

/* Get the matrix order and number of non-zero entries. */
scanf("%ld %*[^\n]", &n);
scanf("%ld %*[^\n]", &nnz);

la     = 20 * nnz;
lindb  = 3 * n;
liwork = 9 * n + 3;

/* Allocate arrays */
b = NAG_ALLOC( n, double);
x = NAG_ALLOC( n, double);

a    = NAG_ALLOC( la, double );
irow = NAG_ALLOC( la, Integer);
icol = NAG_ALLOC( la, Integer);

idiag = NAG_ALLOC( lindb,   Integer);
indb  = NAG_ALLOC( lindb,   Integer);
ipivp = NAG_ALLOC( lindb,   Integer);
ipivq = NAG_ALLOC( lindb,   Integer);
istr  = NAG_ALLOC( lindb+1, Integer);

iwork = NAG_ALLOC( liwork, Integer);

if( (!b) || (!x) || (!a) || (!irow) || (!icol) || (!idiag) || (!indb) ||
(!ipivp) || (!ipivq) || (!istr) || (!iwork) ) {
printf("Allocation failure!\n");
exit_status = -1;
}

/* Initialise arrays */
for ( i = 0; i < n; i++ ) {
b[i] = 0.0;
x[i] = 0.0;
}

for ( i = 0; i < la; i++ ) {
a[i]    = 0.0;
irow[i] = 0;
icol[i] = 0;
}

for( i = 0; i < lindb; i++ ) {
indb[i]  = 0;
ipivp[i] = 0;
ipivq[i] = 0;
istr[i]  = 0;
idiag[i] = 0;
}
istr[lindb] = 0;

for( i = 0; i < liwork; i++ ) {
iwork[i] = 0;
}

/* Read the matrix A */
for ( i = 0; i < nnz; i++) {
scanf("%lf %ld %"NAG_IFMT, &a[i], &irow[i], &icol[i] );
}
scanf("%*[^\n] ");

/* Read the RHS b */
for ( i = 0; i < n; i++) {
scanf("%lf", &b[i] );
}
scanf("%*[^\n] ");

/* nag_enum_name_to_value (x04nac): Converts NAG enum member name to value */
scanf("%39s %*[^\n]", nag_enum_arg);
method = (Nag_SparseNsym_Method) nag_enum_name_to_value( nag_enum_arg );

/* Read algorithmic parameters */
scanf("%ld %lf %*[^\n]", &lfillg, &dtolg);

/* nag_enum_name_to_value (x04nac): Converts NAG enum member name to value */
scanf("%39s %*[^\n]", nag_enum_arg);
pstrag = (Nag_SparseNsym_Piv) nag_enum_name_to_value( nag_enum_arg );

/* nag_enum_name_to_value (x04nac): Converts NAG enum member name to value */
scanf("%39s %*[^\n]", nag_enum_arg);
milug = (Nag_SparseNsym_Fact) nag_enum_name_to_value( nag_enum_arg );

/* Read algorithmic parameters */
scanf("%ld %lf %ld %*[^\n]", &m, &tol, &maxitn);
scanf("%ld %ld %*[^\n]", &nb, &nover);

/* Allocate arrays */
dtol  = NAG_ALLOC( nb,   double );
istb  = NAG_ALLOC( nb+1, Integer);
lfill = NAG_ALLOC( nb,   Integer);
npivm = NAG_ALLOC( nb,   Integer);

pstrat = (Nag_SparseNsym_Piv *) NAG_ALLOC( nb, Nag_SparseNsym_Piv);
milu   = (Nag_SparseNsym_Fact *) NAG_ALLOC( nb, Nag_SparseNsym_Fact);

if ( (!dtol) || (!istb) || (!lfill) || (!npivm) || (!pstrat) || (!milu) ) {
printf("Allocation failure!\n");
exit_status = -1;
}

/* Initialise arrays */
for( i = 0; i < nb; i++ ) {
dtol[i]  = 0.0;
istb[i]  = 0;
lfill[i] = 0;
npivm[i] = 0;

pstrat[i]  = 0;
milu[i]    = 0;
}
istb[nb] = 0;

/* Define diagonal block indices.
* In this example use blocks of MB consecutive rows and initialise
* assuming no overlap.
*/
mb = (n + nb - 1)/nb;
for ( k = 0; k < nb; k++) {
istb[k] = k * mb + 1;
}
istb[nb] = n + 1;

for ( i = 0; i < n; i++) {
indb[i] = i + 1;
}

/* Modify INDB and ISTB to account for overlap. */
overlap(&n, &nnz, irow, icol, &nb, istb, indb, &lindb, &nover, iwork);

/* Set algorithmic parameters for each block from global values */
for (k = 0; k < nb; k++) {
lfill[k]  =  lfillg;
dtol[k]   =  dtolg;
pstrat[k] =  pstrag;
milu[k]   =  milug;
}

/* Initialise fail */
INIT_FAIL(fail);

/* Calculate factorization
*
* nag_sparse_nsym_precon_bdilu (f11dfc). Calculates incomplete LU
* factorization of local or overlapping diagonal blocks, mostly used
* as incomplete LU preconditioner for real sparse matrix.
*/
nag_sparse_nsym_precon_bdilu(n, nnz, a, la, irow, icol, nb, istb, indb,
lindb, lfill, dtol, pstrat, milu, ipivp,
ipivq, istr, idiag, &nnzc, npivm, &fail);

if( fail.code != NE_NOERROR ) {
printf("Error from nag_sparse_nsym_precon_bdilu (f11dfc).\n%s\n\n",
fail.message);
exit(-2);
}

/* Initialise fail */
INIT_FAIL(fail);

/* Solve Ax = b using nag_sparse_nsym_precon_bdilu_solve (f11dgc)
*
* nag_sparse_nsym_precon_bdilu_solve (f11dgc): Solves real sparse
* nonsymmetric linear system, using block-jacobi preconditioner
* generated by f11dfc.
*/
nag_sparse_nsym_precon_bdilu_solve(method, n, nnz, a, la, irow, icol, nb,
istb, indb, lindb, ipivp, ipivq, istr,
idiag, b, m, tol, maxitn, x, &rnorm,
&itn, &fail);

if( fail.code != NE_NOERROR ) {
printf("Error from nag_sparse_nsym_precon_bdilu_solve (f11dgc).\n\n%s",
fail.message);
exit(-3);
}

/* Print output */
printf(" Converged in %9ld iterations\n", itn);
printf(" Final residual norm = %15.6E\n", rnorm);

/* Output x */
printf(" Solution vector  X\n");
printf(" ------------------\n");
for (i = 0; i < n; i++) {
printf(" %f \n", x[i] );
}
printf("\n");

NAG_FREE(b);
NAG_FREE(x);
NAG_FREE(a);
NAG_FREE(irow);
NAG_FREE(icol);
NAG_FREE(idiag);
NAG_FREE(indb);
NAG_FREE(ipivp);
NAG_FREE(ipivq);
NAG_FREE(istr);
NAG_FREE(dtol);
NAG_FREE(istb);
NAG_FREE(lfill);
NAG_FREE(npivm);
NAG_FREE(pstrat);
NAG_FREE(milu);
NAG_FREE(iwork);

return exit_status;
}

/* ************************************************************************** */

static void overlap(Integer *n, Integer *nnz, Integer *irow, Integer *icol,
Integer *nb, Integer *istb, Integer *indb, Integer *lindb,
Integer *nover, Integer *iwork) {
/* Purpose
* =======
*
* This routine takes a set of row indices INDB defining the diagonal blocks
* to be used in nag_sparse_nsym_precon_bdilu (f11dfc) to define a block
* Jacobi or additive Schwarz preconditioner, and expands them to allow for
* NOVER levels of overlap.
*
* The pointer array ISTB is also updated accordingly, so that the returned
* values of ISTB and INDB can be passed to
* nag_sparse_nsym_precon_bdilu (f11dfc) to define overlapping diagonal
* blocks.
*
* ----------------------------------------------------------------------- */

/* Scalars */
Integer i, ik, ind, iover, j, k, l, n21, nadd, row;

/* Find the number of nonzero elements in each row of the matrix A, and start
* address of each row. Store the start addresses in iwork(n,...,2*n-1).
*/

for ( i = 0; i < (*n); i++) {
iwork[i] =  0;
}

for ( i = 0; i < (*nnz); i++) {
iwork[irow[i]-1] = iwork[irow[i]-1] + 1;
}
iwork[ (*n) ] = 1;

for ( i = 0; i < (*n); i++) {
iwork[(*n)+i+1] = iwork[(*n)+i] + iwork[i];
}

/* Loop over blocks. */
for ( k = 0; k < (*nb); k++) {

/* Initialize marker array. */
for (j = 0; j < (*n); j++) {
iwork[j] =  0;
}

/* Mark the rows already in block K in the workspace array. */
for ( l = istb[k]; l < istb[k+1]; l++) {
iwork[indb[l-1]-1] = 1;
}

/* Loop over levels of overlap. */
for ( iover = 1; iover <= (*nover); iover++) {

/* Initialize counter of new row indices to be added. */
ind = 0;

/* Loop over the rows currently in the diagonal block. */
for ( l = istb[k]; l < istb[k+1]; l++ ) {
row = indb[l-1];

/* Loop over non-zero elements in row ROW. */
for ( i = iwork[(*n)+row-1]; i < iwork[(*n)+row]; i++ ) {

/* If the column index of the non-zero element is not in the
* existing set for this block, store it to be added later, and
* mark it in the marker array.
*/
if ( iwork[icol[i-1]-1]==0 ) {
iwork[icol[i-1]-1] = 1;
iwork[2*(*n)+1+ind] = icol[i-1];
ind = ind + 1;
}
}
}

/* Shift the indices in INDB and add the new entries for block K.
* Change ISTB accordingly.
*/
if ( istb[(*nb)]+nadd-1 > (*lindb) ) {
printf("**** lindb too small, lindb = %ld ****\n", *lindb);
exit(-1);
}

for ( i = istb[(*nb)] - 1; i >= istb[k+1]; i-- ) {
}

n21 = 2 * (*n) + 1;
ik = istb[k+1] - 1;

for ( j = 0; j < nadd; j++ ) {
indb[ik + j] =  iwork[n21 + j];
}

for ( j = k+1; j < (*nb)+1; j++) {
istb[j] =  istb[j] + nadd;
}
}
}
return;
}
```